macOS Monterey (version 12) is the 18th major release of macOS, Apple's desktop operating system for Macintosh computers. The successor to macOS Big Sur, it was announced at WWDC 2021 on June 7, 2021, and will be released on October 25, 2021. A beta version of macOS Monterey was released to developers enrolled in the Apple Developer program on June 7, 2021. A public beta version was released at the beginning of July 2021.ng the user's iCloud photos and Messages attachments.